Methicillin-resistant Staphylococcus aureus (MRSA) is a bacterium resistant to the antibiotic methicillin. Staphylococcus aureus, sometimes referred to simply as “staph,” or “staph A” is a common bacterium found on the skin of healthy people. If staph gets into the body it can cause a minor infection such as boils or pimples or serious infections such as pneumonia or blood infections.
One antibiotic commonly used to treat staph infections is methicillin. While methicillin is very effective in treating most staph infections, some staph bacteria have developed a resistance to methicillin and can no longer be killed by this antibiotic. The resistant bacteria are called methicillin-resistant staphylococcus aureus or MRSA.
Current methods for the detection of staph and MRSA may not be performed directly from blood culture bottles. In the methods, a sample is taken from a positive blood culture bottle and plated onto culture medium and grown overnight. A colony is removed from the culture medium and its species determined by a coagulase test. If it is coagulase-positive, the organism is staph A, if it is coagulase-negative, it is another species of Staphylococcus. Once the organism is determined to be staph A, a colony is plated onto culture medium containing methicillin and grown for a minimum of 24 hours. If the organism grows, it is MRSA and if it does not grow, it is methicillin-sensitive Staphylococcus aureus (MSSA). Thus, such methods are time-consuming and involve many steps, including preparing a secondary culture plate.